Multi GPU is going to change in the future once DX12 and Vulkan support it on a regular basis, especially if it works well for mixing cards.
I wouldn't make any decision based on expecting multi-GPU support though, and now that I think about it I don't know if you require an SLI bridge for SFR (Split Frame Rendering) to work. They did test using an NVidia card and an Intel iGPU so I guess not.
Other:
1) 144FPS is not practical to expect in many games.
2) If you have screen tear issues, then forcing "Half" Adaptive VSYNC might be the best choice. This synchs to 72FPS with 144Hz monitors, but turns VSYNC OFF (to avoid stuttering) below 72FPS.
3) If deciding between the RX-480 and GTX1060 I'd go with NVidia. The RX-480 will improve with DX12 titles, but I can't recommend basing much of your decision on how it WILL perform in SOME future games.
Go with the games you intend to play over the next year or so.
4) THE DIVISION benchmark:
http://www.tomshardware.com/reviews/nvidia-geforce-gtx-1060-pascal,4679-5.html
NVidia is about 15% faster.
I would still consider the RX-480 if their is a large price difference.
So you get screen tear but not STUTTER in that case.
5) AVERAGE difference (mostly current/older games):
https://www.techpowerup.com/reviews/MSI/GTX_1060_Gaming_X/24.html
Roughly 10% difference.
HITMAN - SAME performance!
Crysis 3 - 20% faster on GTX1060
Driver updates may help, and again the RX-480 should improve more compared to the GTX1060 but some of that will simply CLOSE THE GAP. They are fairly close overall, so maybe let BUDGET decide things.
The GTX1070 is better still, but I assume it's over budget. You aren't in the USA so I'm estimating what you can afford.
Update:
The above results assume a good CPU. If yours is lower then if a CPU bottleneck occurs in a game the numbers will be similar between cards.